Update own firmware

Hi, I wanto to have the posibility to update the firmware in my AT89C51ED2. For that, I've done two codes, the BASIC CODE (from 0x0000 to 0x3FFF) and the EXTENDET CODE (from 0x4000 to 0xFFFF). When I want to do a firmawe update I erase only the blocks from 0x4000 to 0xFFFF, so I've always a BASIC CODE to minimal operation.

There are many difference between these codes, but one of them is how to manage the interrups. Both have the same hardware interrupt vectors but not the same interrupt routine.

For example, the BASIC CODE has in the UART interrupt this code:

void uart_interrupt(void) interrupt 4
{
        if(kernel_new_prog_enable == 1)
        {
                // Jump new interrupt
                int_uart_interrupt();
                return;
        }
        if(RI == 1)
        {
                RI = 0;
                uart_data = SBUF;

                // Implementation of modbus RTU
                // Initiate with basetime
                t0_init(0xFF-((UART_TXRX_RATE*2)>>8), 0xFF-(UART_TXRX_RATE*2));
                // Accepts what is comming
                uart_buffer[uart_index] = uart_data;
                uart_index++;
                P0_0 = ~ P0_0;
        }
        else
        {
                TI = 0;
                if(uart_index < uart_frame)
                {
                        SBUF = uart_buffer[uart_index];
                        uart_index++;
                }
                else
                {
                        uart_index = 0;
                }
        }
}

void int_uart_interrupt(void)
{
        return;
}

and the EXTENDET CODE has this interrupt function:

void uart_interrupt(void) interrupt 4
{
        if(RI == 1)
        {
                RI = 0;
                uart_data = SBUF;

                // Implementation of modbus RTU
                // Initiate with basetime
                t0_init(0xFF-((UART_TXRX_RATE*2)>>8), 0xFF-(UART_TXRX_RATE*2));
                // Accepts what is comming
                uart_buffer[uart_index] = uart_data;
                uart_index++;
                P0_0 = ~ P0_0;
        }
        else
        {
                TI = 0;
                if(uart_index < uart_frame)
                {
                        SBUF = uart_buffer[uart_index];
                        uart_index++;
                }
                else
                {
                        uart_index = 0;
                }
        }
}

Both funciton are the same, the only difference is at the beginning, the condition statement witch ask if the EXTENDET CODE exists. Offcourse if the EXTENDET CODE exists, the compiler makes a LCALL to the position of the function

int_uart_interrupt

. I've forced that this function code shoud be stored at the address 0x4023, and I've shifted the interrupt vector address in the EXTENDET CODE to 0x4000, so the UART interrupt is stored now in 0x4023. In the address 0x4023 is a LJMP to where the EXTENDET CODE UART interrupt function is. At the moment this is working well, but is there a simple way to do that? Hope you understand my English and my code, and also my explanation. Thanks. Regards, Piero Codas